1. Field
This invention relates to ski bindings. More particularly, the invention relates to ski bindings which are adapted to be used for both downhill skiing and cross-country/telemark skiing.
2. State of the Art
Bindings for attaching boots to alpine, i.e., downhill skis have evolved from simple straps into which the boot is placed to complex safety bindings which rigidly clamp the boot to the ski. These safety bindings have apparatus which are set to release the boot at predetermined excessive forward and transverse forces.
On the other hand, cross-country and telemark skiing is performed with the heel of the boot free to rotate upward and forward during the skier's stride. Present bindings retain the toe of the boot sole in a rigid or semi-rigid position, and rely upon sole flexure to permit the boot to rotate about the toe. Alternately, the binding and the toe of the sole may rotate together.
The resurgence of telemark skiing over the past ten years has spurred an intensive developmental race for technological advancement of telemark ski equipment. In the late 1970's when "cross-country" skiers began telemarking on the slopes of lift serviced areas, new demands were made of the cross-country ski equipment available at the time. Numerous changes were made in the boot design to make it more like that of an alpine boot including a stiffer sole and thicker leather for better torsional control and a higher, stiffer cuff. This was the birth of a new sport: telemark skiing.
Over the past ten years, many skiers have turned to telemark skiing as an alternative to alpine skiing and in so doing have made new demands on their equipment. The ski industry responded by beefing up three-pin boots and bindings to support a more aggressive method of skiing. The three-pin system, originally intended to be used in cross-country skiing, was restructured for telemarking. This restructuring included placing stiff plastic cuffs and a stiffer sole in the boots and using stronger materials for the binding in an attempt to make the three-pin boot and binding system withstand the demands traditionally met by alpine skiing equipment.
There are several obvious advantages to using a telemark system which explain its recent rise in popularity in both the U.S. and Europe: (1) telemark equipment is very light weight, (2) it provides for a very efficient means of mobility with its flexible toe, and (3) it performs well for skiing downhill through powder snow. However, in the use of a conventional telemark system when skiing at lift serviced resort areas, where slopes are often icy or packed powder, or on dangerous ice clad slopes in an alpine environment, the three-pin telemark boot and binding system is entirely ineffective in holding an edge, when compared to a conventional alpine skiing system.
The three-pin binding is still held as the best system available when the advantage of having a flexible toed boot is desired for cross-country travel and telemark skiing. However, the problem with the three-pin system is that it is torsionally unresponsive to the skier, i.e., it has a certain amount of twist in the sole of the boot which makes it difficult to hold an edge on packed powder or icy slopes. Although the ski industry has made the boots stronger, higher, and more rigid with plastic inserts and improved structural characteristics, the fundamental design of the binding has not changed.
The growing number of telemark skiers that frequent lift-serviced alpine resorts or engage in "extreme skiing" are pushing to the limits of their abilities to meet the challenge of keeping up with the abilities of alpine skiers. In order for "tele-skiers" to exhibit comparable control to that of an alpine skier, there must be an overall change in the technology of telemark equipment.
Another form of cross-country/downhill touring system is the alpine touring binding which is designed to be used with rigid soled alpine boots. This style of touring is currently very popular in Europe. There are typically three major problems with the alpine touring bindings on the market today. First, the alpine touring binding is relatively heavy. Most of the alpine touring systems weigh close to five pounds per pair. Obviously, considerably more energy is required for the skier to make a touring ascent using a heavy binding than it does with a lightweight binding.
The second major problem with alpine touring systems is that they do not perform well in a cross-country mode. With the heel of the boot free, the binding provides very little resistance to raising the heel from the ski, which is fine for touring or walking on flat land or climbing a hill, but for skiing alpine style, down a steep face between the flat sections of a traverse, the absence of a substantial resistance to forward lean would increase the possibility of doing a "face plant" or worse. To avoid this, the skier would either have to stop and lock the heel of the boot down every time a downhill section was encountered or resort to using a telemark turn. Although telemark turning with alpine touring binding systems avoids the face plant problem, performing a telemark turn without the benefit of utilizing the flexible toe of a flexible-toed boot, and without any reasonable forward lean resistance provided by the binding, forces the skier to make turns on the tip of the toe instead of on the ball of the foot of the uphill ski. Telemark turning on the tip of the toe is awkward and unstable, resulting in an overall poor skiing performance which is less than desirable when confronted with a difficult traverse on top of a steep icy corniced ridge.
The third major problem with alpine touring bindings is related to the release capabilities of the bindings. Some alpine touring bindings require the skier to stop and take off the ski in order to change skiing modes, and some are not releasable in the touring mode. Others are releasable transversely at the heel which is more likely to cause skier injury than a binding that releases transversely at the toe.
In cross-country/telemark skiing, control of the skiis requires that torsional movement of the boot about the axis parallel with the ski is minimized so that each ski can be firmly directed by maintaining the desired rigidity between boot and ski. Bindings mounted at or forward of the toe permit undesirable torsional bending forces acting through the toe sections of the boot and transverse flex of the boot with respect to the ski axis.
In toe-connected boots, torsional rotative forces are transmitted from the skier's ankle through the length of the boot. The fixed toe acts as an axis of rotation, and the relatively long distance from ankle to toe is the radius of rotation. The torque exerted on the toe by a given transverse force F is the moment of inertia times angular acceleration. The moment of inertia is proportional to the square of the radius of rotation. The bending and twisting moments are absorbed primarily by the boot sole and may be very high, resulting in undesirable transverse flexure and torsional twisting about the longitudinal axis of the boot. Such flexure and twisting results in diminished control of the ski edges on the skiing surface.
The sport that telemarking has become today demands even more of its equipment including the need for the edge control capability of an alpine system along with the light weight, efficient mobility of a cross-country ski system. Despite all of the efforts made in the ski industry, the ultimate telemark system has yet to be developed.